As may be appreciated, several partly contradictory criteria come to the fore in the consideration of transparent panes for use as a window in the foldable top for a convertible car. For one thing, as the use suggests, the pane must display good optical characteristics, thereby to guarantee not only good viewing but distortion-free viewing. The pane, also, must be sufficiently stiff so that in its stretched state, that is, when the foldable top is in place to enclose the passenger compartment, the pane will be substantially free or as free as possible of any undulations as may be occasioned by a folding of the pane when the foldable top is in a retracted position. On the other hand, the pane must be characterized by sufficient flexibility so that it may follow the folding process as the convertible top is retracted from the passenger compartment enclosing position. This is the case since the pane is integrated in the convertible top and buckling of the pane is to be avoided. The pane, further, must display good stretch resistance, and the optical characteristics should not be deleteriously effected by a scratched surface. The characteristics, finally, should remain during a long period of time under temperature conditions which may range from -40.degree. C. to +80.degree. C.
At this time there is no pane known to the prior art that includes all of the required characteristics, let alone these characteristics in optimum fashion. To this end, for example, if the characteristic of flexibility is increased to follow the folding process, it oftentimes is increased at the sacrifice of its optical characteristics, and vice versa. Oftentimes, however, the flexibility of the pane leaves something to be desired. Moreover, in the case of all plastic panes, the scratch resistance of the surfaces is poor, so that after use, the optical characteristics are poor. These characteristics are even more strongly affected by extended use, and it is not uncommon that the theretofore transparent pane becomes somewhat translucent. The disturbing effect on transparency has been discovered during use of panes, such as panes of polyvinyl chloride of about 1.5 mm in thickness.